Methods of making guns



United States Patent 3,382,556 METHGDS 0F MAKING GUNS Bernard Maillard, Geneva, Switzerland, assignor to Brevets Aero-Mecaniques S.A., a society of Switzerland Filed June 24, 1966, Ser. No. 560,152 Claims priority, application Luxembourg, July 9, 1965,

49, 4 Claims. (Cl. 29-11) ABSTRACT OF THE DISCLOSURE The present invention relates to the manufacture of guns the ammunition of which comprises a cartridge case to ensure a sufficient obstacle to the outflow of the propelling powder gases toward the outside and the rear.

The invention is more especially, but not exclusively, concerned with automatic guns of small or medium calibre (i.e. mm., mm. or even more), the ammunition of which comprises a cartridge case carrying the projectile at the front thereof.

It has already been proposed to form, in the inner wall of the cartridge chamber (this term designating the housing, located at the rear of the gun barrel in which said cartridge case has to be engaged) of the guns in question, a hard superficial layer obtained by treatment, in particular by nitriding, of the metal of which the cartridge case is made.

On the other hand it has also been proposed to provide, in all of the cartridge chamber, at least one recess into which the burnt powder gases flow during firing, thus exerting, on the outer wall of the cartridge case, a counterpressure tending to separate said cartridge case from the corresponding Wall of the cartridge chamber.

It will be understood that, when it is desired to apply both of the features above referred to, it seems obvious first to make the recess and to perform the hardening treatment only subsequently, so that the hard superficial layer formed on the inner wall of the cartridge chamber does not constitute a difiiculty in machining said cartridge chamber.

Now, experience has taught that, especially when the hardening treatment is a nitriding treatment, if the operations are performed in the order above mentioned, friable compounds are formed along the outer edges of the recesses which cause a quick deterioration of said edges resulting in a saw-tooth shape, which leads to a deterioration of the cartridge cases.

The object of the present invention is to obviate this drawback.

The inner wall of the cartridge chamber of a gun of the type above referred to comprises at least one recess, preferably in the form of a groove, into which fiow the powder gases formed during firing which inner wall is subjected to the hardening treatment, preferably a nitriding treatment.

According to the present invention this housing is formed after having performed at least a part of said hardening treatment, which avoids the formation of brittle compounds in the junction zones between the inner wall "ice of the cartridge chamber and the above mentioned recesscs, while leaving the benefit of the hardening treatment to the portions of the inner wall of the cartridge chamber in contact with the cartridge case.

A preferred embodiment of the present invention will be hereinafter described with reference to the appended drawings, given merely by way of example, and in which:

FIG. 1 is an axial sectional view of the cartridge chamber (containing a cartridge case) of a gun according to the present invention;

FIGS. 2 and 3 are views showing on an enlarged scale the portions I and II of FIG. 1 surrounded by dotted lines;

FIGS. 4, 5 and 6 diagrammatically show the outline of one of the grooves cut in said cartridge chamber (only the front and rear ends of these grooves being shown);

FIGS. 7 and 8 are diagrammatic partial sections along planes perpendicular to the axis of the gun barrel showing, respectively, a groove 2 according to the invention and a groove machined before nitriding or electrolytic lining treatment.

It will be supposed that the following description relates to an automatic gun of 20 mm. calibre.

This gun is made of any suitable, and for instance conventional, general structure.

Concerning the cartridge chamber 1 of said gun, it comprises a plurality of grooves 2 of, for instance, 0.5 mm. depth and 1 mm. width, preferably obtained by electroerosion, into which the burnt powder gases flow during firing from the front of cartridge case 3, in order to exert on the external wall of the cartridge case a counterpressure tending to detach or separate this wall from the wall of the cartridge chamber.

These grooves 2 start, at the front, downstream of the front edge of cartridge case 3 and they end, at the rear, for instance, at a distance of 35 mm. ahead of the rear end of the cartridge case, so as to form a wall at right angles to the gun axis.

According to the present invention these grooves 2 are formed by electro-erosion, after having subjected the walls of the cartridge chamber, after machining, to a treatment, in particular as it will be hereinafter supposed, a nitriding treatment, producing a hard superficial layer 4 (for instance of a thickness averaging A0 of a millimeter) of a hard iron nitride Fe N on the inner wall (which surrounds a cartridge case when the cartridge is fitted in chamber 1) of said cartridge chamber. This hardened layer may be lined with an electrolytic layer of chromium 5 of, for in stance, of a millimeter.

Advantageously, grooves, substantially of equal depths, are formed preferably over the whole length.

The method according to the preferred invention avoids the formation (which would take place at the edges of the grooves if, as shown by FIG. 8, said grooves were treated to harden them only after the cutting of said grooves) of a nitrogen saturated iron nitride, the formula of which is Fe N, which would make the edges of said grooves brittle and friable and would lead to the formation of saw-teeth detrimental for the cartridge cases.

It will be noted that the grooves cut as above stated are terminated at their ends by walls 6 substantially perpendicular to the axis of the gun barrel, instead of being connected with the wall of the cartridge chamber through a slope, as this would be case, for instance if the grooves were obtained by removal of metal turnings. Now this arrangement facilitated, for the gases having entered the grooves, their outflow as soon as the pressure dropped in the gun barrel.

Of course the shape of the cross section of the grooves may be chosen at will.

For instance they may be limited laterally, by longitudinal parallel lines (FIG. 4), or by lines diverging from 3 each other from the front toward the rear, for instance along the directrices of the cartridge chamber (FIG. 6).

The grooves might be narrowed at the front over a length of, for instance, 5 mm. and then have, toward the rear, a constant Width. Thus their capacity would be great, whereas the outflow of the gases, and therefore the pressure drop, would be delayed by the narrow width of the passage toward the outside.

In a general manner, while the above description discloses what are deemed to be practical and efiicient embodiments of the present invention, said invention is not limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the invention as comprehended within the scope of the appended claims.

What I claim is:

1. A method for forming gas receiving means in the walls of a cartridge case, comprising the steps of:

(a) subjecting the inner wall of said cartridge chamber to a thermal hardening treatment to a given depth, and subsequently,

(b) forming, by a material removing procedure, at least one recess in said inner wall, to a depth such that the recess passes through at least a major part of said given depth, said recess positioned to receive gases from the cartridge after it is fired to facilitate retraction of the cartridge case, whereby the portions of the inner wall remaining after the formation of 5 the said recess and adapted to contact the cartridge case are hardened, and whereby the zones connecting the recess to the inner wall are substantially free of brittle compounds. 2. A method according to claim 1 wherein the step of m forming the recess includes forming a longitudinal groove. 3. A method according to claim 1 wherein the step of hardening the inner wall includes a nitriding treatment.

4. A method according to claim 1 wherein the step of forming the recess in the inner wall of the cartridge 15 chamber includes an electro-erosion procedure.

References Cited UNITED STATES PATENTS RICHARD H. EANES, JR., Primary Examiner.

UNITED STATES PATENT OFFICE f CERTIFICATE OF CORRECTION Patent No. 3,382,556 May 14, 1968 Bernard Maillard It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

l i Column 3 line 18 after "cartridge" insert chamber of 'a--"-=g'un of the type adapted to receive a cartridge Signed and sealed 7th day of April 1970.

( ET- L) Attest:

y Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

